In recent years, noncontact power transfer systems that wirelessly supply electric power to portable devices, such as smartphones and laptop personal computers, have been in practical use. Examples of the noncontact power transfer systems include one described in Patent Document 1.
Patent Document 1 discloses a noncontact power transfer system of an electromagnetic induction type. The noncontact power transfer system of the electromagnetic induction type includes a transmitting device and a receiving device. The transmitting device and the receiving device include a transmitting coil and a receiving coil, respectively, between which electric power is transferred by electromagnetic induction.
Patent Document 2 discloses a noncontact power transfer system of an electric field coupling type. The noncontact power transfer system of the electric field coupling type includes a transmitting device and a receiving device. The transmitting device and the receiving device include a transmitting electrode and a receiving electrode, respectively, between which electric power is transferred by electrostatic induction.
Patent Document 1: Japanese Patent No. 3344593.
Patent Document 2: International Publication No. WO 2011/148803.
In a receiving device of a noncontact power transfer system, an overvoltage may occur between receiving electrodes when the receiving device attached to a transmitting device for power transfer is removed therefrom. The receiving device may include a protection circuit for preventing damage to the receiving device caused by the overvoltage. After the removal of the receiving device, the transmitting device is always required to stop the power transfer.